The present invention relates to a method for preparing powder coating composition. Further in detail, the powder coating composition is suitable for coating of a precoat metal (hereinafter referred to as xe2x80x9cPCMxe2x80x9d).
Hitherto, there have been many proposals as to a powder coating composition. In JP-A-1-103670, for example, there is described a thermosetting powder coating composition comprising a fluorine-containing copolymer containing chlorotrifluoloethylene as the main component and a curing agent.
A coating film obtained from the powder coating composition described in the above-mentioned publication has high gloss and good weather resistance. There is a problem, however, that the coating film is inferior in bending resistance because the fluorine-containing copolymer is crosslinked by the curing agent, and thus the coating film is difficult to be employed for an application such as PCM which need to be subjected to post processing such as bending.
The present inventors have found that a powder coating composition comprising a specific powder which contains specific amounts of a specific vinylidenefluoride copolymer and a specific methyl methacrylate copolymer can provide a coating film being excellent particularly in bending resistance.
Namely, an object of the present invention is to provide a method for preparing powder coating composition which is superior in dispersibility of pigment, weather resistance, appearance and stain-proofing property and particularly excellent in bending resistance, which makes it possible to give a coating film being hardly cracked during bending process of the metal plate with the film thereon in the application for PCM.
The present invention relates to a powder coating composition comprising a powder which contains
100 parts by weight of a vinylidene fluoride copolymer having a melting point of not higher than 150xc2x0 C., a crystallinity of not higher than 35% and a weight average molecular weight of from 1xc3x97104 to 5xc3x97105 and
10 to 400 parts by weight of a methyl methacrylate copolymer having a glass transition temperature of not higher than 110xc2x0 C. and a weight average molecular weight of from 1xc3x97104 to 5xc3x97105;
an average particle size of particles constituting the powder being from 1 to 100 xcexcm and an apparent density of the powder being from 0.2 to 1 g/ml.